1. Field of the Invention
The present invention relates to electrical switching apparatus, such as, for example, circuit breakers and, more particularly, to circuit breakers employing a slot motor.
2. Background Information
Circuit breakers, such as molded case circuit breakers, include at least one pair of separable contacts. A first contact is fixed within the molded case housing and a second movable contact is coupled to an operating mechanism. These separable contacts are in electrical communication with either the line or the load coupled to the circuit breaker. The operating mechanism moves the movable contact between a first, open position wherein the movable contact is spaced from the fixed contact, and a second, closed position wherein the fixed and movable contacts are in contact and electrical communication. The operating mechanism may be operated manually or by a trip mechanism.
The exterior walls of molded case circuit breakers have typically been a weak link for case strength and a limiting factor in increasing the interrupting ratings of circuit breakers.
In order to enhance the speed of separation of the separable contacts, the contacts may be disposed within a slot motor, which increases interruption performance. The slot motor is a ring or loop-shaped device made of magnetically permeable material (e.g., steel), which surrounds the contacts and the movable contact arm of the circuit breaker. When the circuit is live, an electrical arc may be drawn between the electrical contacts during separation. The electrical current interacts electromagnetically with the slot motor to induce a magnetic field in the magnetic material of the slot motor, which, in turns, interacts with the separating contacts and the movable contact arm to accelerate the contact opening process. Examples of slot motors are disclosed in U.S. Pat. Nos. 4,375,021; 4,546,336; 4,546,337; 4,549,153; 4,970,482; 5,694,098, and 6,281,459.
Slot motors generally have two assemblies, an upper assembly and a lower assembly. Both upper and lower assemblies include a corresponding housing and a plurality of plates composed of the magnetically permeable material. The lower assembly is disposed below the fixed contact. As shown in FIG. 1, the upper assembly is an inverted U-shaped assembly having a housing assembly 1 and a plurality of plates 2, forming a bight portion 3 and two legs 4,5. The upper slot motor assembly is structured to be disposed over the movable contact (not shown) wherein the tips of the upper assembly legs 4,5 contact the lower slot motor assembly (not shown). The upper assembly legs 4,5 have an extended length to accommodate the path of travel of the movable contact arm (not shown). That is, the movable contact (not shown) is disposed between the upper assembly legs 4,5 and as the movable contact moves between the first, open position and the second, closed position, the movable contact moves from a position adjacent to the upper assembly bight portion 3 to a position adjacent the tips of the legs 4,5. Accordingly, the legs 4,5 have a sufficient length to accommodate the path of travel of the movable contact arm.
There is room for improvement in electrical switching apparatus, such as circuit breakers, employing a slot motor.